1. Field of the Invention
This invention relates generally to switching of optical signals; and in particular, to the spatial routing of optical signals transmitted in optical communication networks and optical signal processing.
2. Background of the Invention
Optical fibers are used as the physical media for transmitting optical signals in a variety of commercial and military applications. As the data rates of information continue to grow, it becomes increasingly difficult for conventional electronic switching systems to handle higher bandwidths. In addition, the required conversion between optical and electrical signals restricts the data format and increases costs. All-optical routing/switching technologies, characterized by high xe2x80x9cdata transparency,xe2x80x9d can switch or transfer optical signals from one transmission channel to another while the signals remain in optical form.
Several multiplexing schemes have been developed in fiber optic interconnection networks, including time-division multiplexing (TDM), wavelength-division multiplexing (WDM) and space-division multiplexing (SDM). Space-division switching is considered to be one of the most important fiber optic routing schemes. Major applications of space-division photonic switches are in fiber optic communication networks, optical gyroscopes, optical signal processing, and micro/millimeter wave signal distribution for phased-array radar systems.
A wide variety of electromagnetic field-controlled optical switches are commercially available. They are based on mechanical, electro-optic, thermo-optic, acousto-optic, magneto-optic, and semiconductor technologies. Each switching technology has its own advantages, but also has drawbacks as well. For example, mechanical switches are the most widely used routing components and provide very low insertion loss and crosstalk characteristics, but their switching time is limited to the millisecond range. They also have a limited lifetime because motor-driven parts are used. LiNbO3 integrated optic switches, on the other hand, offer nanosecond switching times. However, LiNbO3 switches suffer from the disadvantages of relative large insertion loss (5 dB), high crosstalk (20 dB) and polarization dependency.
Accordingly, efforts continue to develop field-controlled optical switches with lower channel crosstalk, reduced polarization dependent loss, and at least moderate reconfiguration speed. It is recognized that these efforts, when successful, can provide an essential component to fiber communication systems.
3. Solution to the Problem
The present invention employs an optical network of polarization rotator arrays and polarization-dependent routing elements (e.g., birefringent elements or polarized beamsplitters) to achieve an optical routing structure that provides polarization-independent and low-crosstalk switching over a wide operating range of temperatures and wavelengths. This optical switch retains the switched signals in optical format and preserves their optical properties.
This invention describes an optical routing switch for selectively routing an optical signal from any of a plurality of input ports to any of a plurality of output ports. The optical signal at each input port is spatially decomposed into two orthogonally-polarized beams by a first polarization-dependent routing element (e.g., a birefringent element or polarized beamsplitter). Beyond this point, a network of optical switches are placed along the optical paths of the pair of light beams. Each optical switch includes: (1) a polarization rotator that switchably controls the polarization of the input light beams so that both of the emergent beams are either vertically or horizontally polarized, according to the control state of the device; and (2) a polarization-dependent routing element that spatially routes the light beam pair to provide physical displacement based on their state of polarization. The final stage for each output port in the network consists of an array of polarization rotators that changes the polarization of at least one of the light beams, so that the two beams become orthogonally polarized. Finally, a polarization-dependent routing element (e.g., a birefringent element) intercepts the two orthogonally-polarized beams and recombines them to exit at the selected output port.